DESCRIPTION: The long-term objective of the research is to define the role of the prion protein in the neuropathogenesis of strain diversity for the transmissible spongiform encephalopathies (TSEs). Specifically, Dr. Bessen will test the hypothesis that the pathogenicity of TSE strains is determined, in part, by the properties of the prion protein that comprises each strain. In Aim #1, the applicant will develop a fluorometric cell-free conversion assay for PrP-res formation using thioflavin T. In Aim #2, the applicant will utilize an in situ PrP conversion assay to determine the brain distribution and rate of conversion of PrPC to strain-specific PrP-res isoforms. This assay will also be used to define the role of anti-TSE drugs in the conversion reaction, to probe the mechanism of drug inhibition, and to rapidly screen for new inhibitors or accelerators of PrP-res formation. Finally, in Aim #3 the applicant will develop PrP-res fibril extension assays that utilize electron microscopy and high-definition photomicroscopy to examine the kinetics and polarity of PrP-res fibril formation. For each of the aims, the hyper (HY) and drowsy (DY) strains of transmissible mink encephalopathy (TME) will be examined in order to determine the role of strain-specific PrP-res in the neuropathogenesis of strain diversity.